Piston.



No.693,085.' v Patented Feb. ll, 1902.

S.- TRETHEWEY. n

PISTUN.

(Application med Feb. 7, 1901;) (No Model.)

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UNITED STATES PATENT EEICE.

SAMUEL TRETHEWEY, OF PITTSBURG, PENNSYLVANIA.

PISTON.

SPECIFICATION forming' part of Letters Patent No. 693,085, dated February 11, 1902.

Application filed February 7, 1901l Serial No. li6,309. (No model.)

T0 @ZZ whom, t may concern,.-

Be it known that I, SAMUEL TRETHEWEY, a citizen of the United States of America, and a resident of the city of Pittsburg, county of Allegheny, Commonwealth of Pennsylvania, have invented certain new and useful Improvements in Pistons, of which the following is a specification.

Referring to the drawings which make part of this specification, Figure I is an elevation of my improved piston, partially cut away to show parts. same with the front plate removed. Fig. III shows my improved set ring. Fig. IV is a sectional view of the same along the line a a in Fig. III; and Fig. Vis a sectional detail view of my packing-rings, showing the same connected by lip and recess.

Generally stated, my invention consists in an improved piston so constructed that the packing or bearing surface can easily be adjusted to take up wear and at all times to snugly fit the bore of the cylinder. The arrangement of back and front plates is such that under no circumstances can the wearing away of the bearing surfaces allow said plates to come into contact with the cylinderbore.

My invention is applicable in all cases where a piston traversing the interior of a cylinder is utilized, and in case the stroke is very short, as in a valve, I provide the bearing-surface with projections or tongues at its front and rear edges, thus giving the piston a longer bearing-surface and preventing the excessive friction usually attendant upon the use of a narrow piston.

The following is a detailed description of my invention, reference being had to the drawings.

l is the piston rod. thereon.

3 is the back plate of the piston, which is slipped down over the piston-rod l and bears against collar z..

4 is the front plate, also litted to slip over piston-rod 1.

5 is a split set-ring, preferably made of spring-steel, intended to be seated in the annular recess formed by the offsets 6 6a in plates Sand 4: when said plates are in position, as in 2 is a collar fixed Fig. II is a plan view of the 7 a are split bearing-rings or packing, constructed in the form of two rings with their adjacent surfaces adapted to fit snugly together and their opposite edges indented to forni a series of projections 8 S, the use of which projections is hereinafter described, said opposite edges of said bearing-rings extending over the edges of the back and front plates of the piston and being between the same and the bore of the cylinder, as shown in Fig. I.

9 9 are annular fianges on rings 7 7'ad and are seated in the recess formed by the offsets 6 6 in plates 3 and 4.

Projections 8 8 on ring 7 7 are for use in cylinders where the stroke isv short and the width of the piston is required to be slight, such as when the orifices of a valve are to be alternately opened and closed. In such cases the friction of the piston upon the bore of the cylinder is very great and undue Wear results. By means of these projections or tongues 8 S I procure a much larger bearing-surface for the piston, thus steadying the piston and reducing the'friction, while the indentations between the projections being preferably of a greater area than the projections prevent undue closing of the valve-orices and cause such orices to be exposed in as satisfactory manner as if the entire bearing-surface of the piston were as narrow as my piston between two opposite indentations.

10 is an annular lip (not shown in Fig. I) on one of the split packing-rings, as 7, which lip registers when the members of the piston are assembled with recess l0a in the other packing-ring, as 7a. By means of this arrangement the packing-rings are kept in thesame relative positionand present a regular and smooth surface to the boreof the cylin der. This arrangement ot' lip and recess also prevents the steam from expanding the packing-ring, against which it is directly exerted in a greater degree than the other packingring, in which case anirregular packing-sur- ICO seated in annular oliset 6 in plate 8. The bearing-ring 7 is then rested on offset G, and upon it is placed bearin g-rin g '75. The action of set-ring 5, which is made the same width as the flanges 9 and 9 together, tends to expand the split bearing-rings 7 7% thus enabling them to maintain a snug iit with the cylinder-bore. The rings 7 7a are assembled so that their split portions do not register, thus preventing the formation of an orifice or leak through the piston, the bearingrings being held in a fixed relative position by pin 10 passing through both rings. After the above parts are in place front plate 4 is slipped on, and nut 1l is screwed on the end of piston-rod -l until the plate 4 is forced snugly against plate 3. The width of setring 5 or the combined width of iianges 9 and 9a is slightly less than the width of offsets 6 6, thus leaving set-ring 5 free to expand the bearing-rings 7 7 and keep the same snugly fitting the bore of the cylinder.

I form my set ring preferably of springsteel, and its inner edges are cut into annular offsets or recesses l2 l2, producing the crosssectional form shown in Fig. IV, and the thickness of crosssection of said set ring tapers toward the split ends to increase its spring force. By using this cross-section I find that in case it is desired to spread setriug 5 it can be readily taken out and hammered along its inner surface opposite to the split, thus causing the split to open wider and the ring to expand. Owing to the form of cross-section I use this hammering does not displace the metal of the ring or distor the same, so destroying its fit in the piston, but simply expands the ringin a sym metrical manner. It will thus be seen that in case wear causes my piston to become loose in the bore of the cylinder, so that the expansive force of set-ring5 nolongerkeeps the bearing-rings '7 71L snugly 'against the bore of the cylinder,

it is only necessary to remove the set-ring, expand it by the above described method, and replace it again in the piston, whereupon it will expand the split-bearing-rings when the parts are reassembled, causing said bearing-rings to again t snugly in the bore of the cylinder.

It will readily be seen from the above that myinvention is a great advance over the prior art for the following reasons inter alia: My arrangement of split bearing-rings enables meto at all times maintain a snug fit between the piston and the bore of the cylinder, wear being easily taken up by the expanding force of set-ring 5, this set-ring itself being easily expanded to increase its spring force when the wear has become too great to be taken up by it in its original condition. Again, there is no possibility in my device of the front and back plates of the cylinder-head coming in contact with the bore of the cylinder, as is often the case in the prior art, thus enabling the immediate bearing-surfaces to be made of different metal, such as brass,than the body of the piston. Again, my form of bearing-surface with indented edges enables me to produce a piston of very narrow width, but capable of doing its work with but little friction, thus making it of great value for use in valves where the piston is of necessity very narrow and the consequent friction between piston and cylinder very great. The arrangement of lip and recess by which the two split packing-rings are held in the same relative position enables the two packing-rings to expand equally when acted upon by the spring setring and also does away with the tendency on the part of the steam to expand the pack- Aprevent such'expansion caused by the steam and to substitute therefor expansion caused by the spring set-ring. The extreme simplicity of my device, consisting of but a few parts solidly constructed, is a great improvement over the other forms of pistons previously used, my invention being cheap in construction, durable in wear, and easily adjustable when in use.

Although I have described my invention minutely, I do not wish to be limited thereby, but claim broadly- 1. In pistons; the combination of front and back plates; 'an annular packing, and an eccentric spring set-ringbearing against the entire inner surface of said packing.

2. In pistons; the combination of front and back plates; an annular packing consisting of two split rings of L-shaped cross-section, and a split set-ring bearing against the entire inner surface of said packing-ring.

3. In pistons; the combination of front and back plates; an annular packing, and a split spring set-ring bearing against the entire inner surface of said packing and having at its inner edges annular'recesses, substantially as and for the purpose set forth.

4. In pistons g the combination of front and back plates; an annular packing having its front and rear edges indented, and a split spring set-ring adapted to bear against the entire inner surface of said packing.

5. In pistons; the combination of front and back plates; an annular packing consisting 'of two split rings having their outer edges indented, and asplit set-ring adapted to bear against the entire inner surface of said packlng. Y

6. In pistons; the combination of front and back plates; an annular packing having its front and rear edges indented, and a split spring set-ring adapted to bear against the entire inner surface of said packing and having at its inner edges annular recesses, substantially as and for the purpose set forth.

IOC

7. In pistons; the combination of front and I Signed by me at Pittsburg, Pennsylvania, back plates; a packing consisting of two setthis 3d day of January, 1901. rings; an annular recess in one 0f said rings; an annularlip on the other of said rings ad apt- 5 ed to register with said recess, and a split Vitnesses:

spring set-ring adapted to bear against the cn- J. BOYD DUFF, tire inner surface of said packing. EDWARD A. LAWRENCE.

SAMUEL TRETHEVEY. 

